The present invention relates to an arrangement for checking the operation of control circuits and is more particularly applicable to printers which have a linear character support.
At the present time, printers which have a linear character support are often preferred to drum printers because of the higher standard of print which they give, despite the fact that the printing control arrangements for them are more complicated.
In linear character support printers, the characters succeed one another opposite print hammers in an order which depends on their respective positions, whereas in drum printers, a single, repeated character is situated in front of all print hammers at a given moment. Linear character support printers require greater control complexity due to the size of the memory needed to memorize the characters which each of the hammers can strike as a function of time and due to the extensiveness of the addressing circuitry associated with the memory means.
In most printers, the complexity is increased further because the pitch of the characters (the distance between them) is different from the pitch of the print hammers. The result of this difference is that, at any given moment, only a certain number of hammers coincide with characters on the belt, this number depending on the total number of characters and on the ratio between the pitch of the characters and the pitch of the hammers. It is therefore possible to formulate a law which governs the way in which the hammer/character coincidences follow one another cyclically until all the characters have coincided with all the hammers.
To clarify the following text, a cycle is defined as the time T which elapses between two characters which follow one another on the belt coinciding with the same hammer. A sub-cycle is defined as the interval of time separating two series of simultaneous coincidences between hammers and characters.
In printers having a linear character support which moves at a constant speed past a row of N hammers that are actuated by strike amplifiers, it is desired that there should be on the one hand k simultaneous, cyclically repeated coincidences between characters and hammers during a succession of sub-cycles, and on the other hand that in the course of m consecutive sub-cycles, each of the N hammers should coincide once with a character, m being the number of sub-cycles in a cycle and being equal to N/k. Furthermore, it is necessary that each hammer which coincides with a character at the beginning of a given sub-cycle in a cycle should coincide with the next character on the support during the corresponding sub-cycle in the next cycle. In such a system, in order to print a predetermined character at a predetermined position, the sub-cycle ms is selected during which the predetermined character is lined-up in front of the predetermined position. During the selected sub-cycle ms, k amplifiers associated with k hammers are lined up with characters, kc being the amplifier associated with the hammer located at the predetermined position. If amplifier kc is energized during sub-cycle ms, the proper character will be printed in the proper position. The selection can be achieved by using a control matrix having m rows (one for each of the m sub-cycles) and k columns (one for each of the k amplifiers and hammers lined-up with characters during each sub-cycle). By selecting the proper row and column and energizing the amplifier corresponding to the intersection of the selected row and column, the proper print hammer can be made to strike the described character.
Print control arrangements which meet the requirements defined above are known. One such arrangement is described in a French patent application No. 73,09686 entitled "An Arrangement for Controlling Print Hammers For a Printer" which was filed on Mar. 19, 1973 in the names of JEAN-PIERRE BRUNIN and JEAN-JACQUES PIERRE ELTGEN.
Once strike orders have been given to a series of strike amplifiers for coinciding hammers and the hammers in question have printed, it is important to check whether the amplifiers have in fact operated the appropriate hammers. Accordingly, each amplifier is fitted with an error detector for generating an error signal in response to erroneous operation. If an error signal is detected, a checking device organized according to the principles of the control matrix can be used to locate the defective amplifier.
The invention can be used for checking the operation of N control circuits each including a detector for generating an error signal in response to erroneous operation. The control circuits are divided into m groups with k control circuits in each group. N gates pass the error signals when enabled. Each detector is connected to a different one of the gates so that the gates are divided into m groups with k gates in each group. First selection means individually enables different ones of the m groups of control circuits and simultaneously enables the gates connected to the detectors of the enabled control circuits during m sub-cycles of operation so that any error signals generated by the detectors are transmitted by the enabled gates. Second selection means select for operation during each sub-cycle from 0 to k control circuits. Error indicator means receive any error signals transmitted by the gate means so that the erroneous operation of control circuits can be recorded.
The control arrangement according to the invention can be used to control a printer having a linear character support which moves at constant speed past a row of N hammers the spacing of which is different from that of the characters. The hammer-strike amplifiers are provided with detectors for detecting operating errors, which make it possible to detect whether an amplifier has in fact operated after having received an order from the strike-control device.
In accordance with another feature of the invention, the arrangement is characterised in that it comprises:
a sub-cycle counter associated with a decoder having m outputs PA1 an error indicator circuit PA1 an error register PA1 an error detection matrix having m rows and k columns, that is to say N locations, which are connected to the N detectors for detecting errors on the part of the strike amplifiers, each of its m rows being connected to one of the m outputs of the decoder, and each of its k columns being connected on the one hand to a location in the error register and on the other hand to the error indicator circuit via an OR circuit, the error register also being connected to the outputs of the sub-cycle counter. These connections as a whole are so arranged that, when an error is detected by the matrix in the ith row and the jth column where 0 .ltoreq. i .ltoreq. m-l, the error indicator circuit indicates 0 .ltoreq. j .ltoreq. k-1 that one of the N amplifiers is not operating and the error register records the values of i and j.